German Patent Publication 3,320,200 (Gehring et al.), corresponding to U.S. Pat. No. 4,558,722 (Gehring et al.), issued on Dec. 17, 1985 discloses an apparatus for the constrained actuation of the clamping system of weft yarn inserting members in shuttleless weaving looms. In such a loom an inserting gripper transports the weft thread to the center of a loom shed where a second gripper, while the loom shed is open, receives the leading end of the weft thread being inserted and pulls it entirely through the shed to the exit side. Thereafter, the beat-up motion by the reed is performed. The reed is connected to the sley that oscillates about its central longitudinal axis driven by the main loom drive shaft for the beat-up motion. The mechanism for controlling the weft clamp on the respective gripper head comprises a control lever or finger that controls the weft clamp. The control lever in turn is connected to one end of a coupling rod that is mounted for a longitudinal motion and for a tilting motion. The other end of the coupling rod is pivoted to a rocker arm or control lever which in turn carries a cam follower roller engaging a control cam driven by a drive shaft which in turn is driven in synchronism with the sley shaft. For transmitting the force of the control cam onto the rocker arm and from the rocker arm onto the coupling rod for the opening of the weft clamp, the entire transmission link or train comprises a plurality of pivot or journal connections in which a certain bearing play exists that cannot be avoided. It is in the nature of such connecting links that the just mentioned play increases with time. This fact is aggravated because the total play of the transmission link results from the sum of the individual plays at all connecting pivots or journals. Thus, the total play tends to become with time an undesirable play because it may interfere with the precise timing of the activation of the weft clamp in synchronism with the gripper movements. Besides, the weft clamp may become worn out before its time. Thus, there is room for improvement.